The present invention relates to a device for spraying powder; more particularly, for spraying powder onto freshly printed sheets, comprising one or more powder supply conduits from which powder is sprayed by means of compressed air for the purpose of preventing the individual sheets from being smudged. The excess powder is drawn off as far as possible by a vacuum system provided through a suction conduit and, further a curtain of blast air is arranged to confine the sprayed powder to a powder spraying zone which is at least the width of the paper sheet, all of which is claimed in German Patent Application No. P 2,207,983.0.
Devices of this general type have the disadvantage that very fine-grained powder is not only sprayed onto the freshly printed sheets but also onto the surrounding machine parts as well and more particularly, onto the conveyor elements used to transport the sheets. The printing plates are subjected to increased wear owing to the undesirable effect of the sprayed powder. This almost inevitably represents an additional problem for the operator. One of the consequences is increased expenditure for maintaining a printing press equipped with a device of this type. Furthermore, it is not possible to recover the powder sprayed outside of the operating zone.
These disadvantages are obviated according to the invention by providing a curtain of blast air, which prevents the powder from escaping, about the powder spraying zone which is at least the width of a printed sheet.